Dispersion strengthened aluminum alloys containing large volume fractions of finely dispersed, insoluble intermetallic particles can be produced by powder metallurgical techniques. Of interest is U.S. Pat. No. 2,963,780, "Aluminum Alloy Powder Product" by J.P. Lyle, Jr. et al. The Lyle et al. invention is directed to hot worked, dispersion hardened aluminum alloy compositions adapted for service at elevated temperatures. These aluminum alloys are produced by atomizing powders which contain very fine intermetallic particles preferably under 0.4 micrometers. The powder is subsequently compacted at high temperature and hot worked by extrusion processes. Thereafter it may be rolled or forged. Alloy compositions are claimed having iron contents of between 5 and 10% by weight, with at least one hardening element selected from the group composed of 0.1 to 10% manganese, 0.1 to 10% nickel, 0.1 to 10% cobalt, 0.1 to 10% chromium, 0.1 to 10% titanium, 0.1 to 10% zirconium, and 0.1 to 10% vanadium, with the total amounts of the hardening elements not exceeding 10% by weight. No example of an aluminum alloy having a nominal 6% iron, 6% nickel, and 2% chromium was discussed therein.
Another typical technique for making such alloys is disclosed in U.S. Pat. No. 3,899,820, "Method of Producing a Dispersion-Strengthened Aluminum Alloy" by P. J. Read, et al., (also herein incorporated by reference). Read, et al., discloses a method of spray casting wherein the atomized aluminum, in the form of a stream of molten alloy, is cooled by high-velocity jets of nitrogen or other suitable gases. The atomized molten droplets are carried to a moving substrate wherein, upon impact, they solidify at extremely high cooling rates as a result of initial gas cooling and secondary cooling from the substrate. In general, Read, et al., discloses the use of alumimun with 0.05 to 25% of alloying constituents. The amount of the alloying constituents is in excess of the equilibrium solubility. Of particular interest is their disclosure of aluminum alloys containing 3 to 15% of transition metals comprising titanium, vanadium, chromium, magnesium, iron, cobalt, nickel, zirconium, niobium, and molybdenum. P. J. Read et al. particularly emphasizes the fact that the process allows the alloying additions to be retained in the super-saturated solid solution or dispersed in very fine, less-than-one micrometer, particles which are beneficial for dispersion strengthening.
While the above alloys disclosed in the reference patent have shown good strength up to 600.degree. F., above this temperature there remains a need for alloys which exhibit good strength. Also of interest is U.S. Pat. No. 4,347,076, "Aluminum-Transition Metal Alloys Made Using Rapidly Solidified Powders and Method" by Ranjan Ray et al. and U.S. Pat. No. 4,104,061, "Powder Metallurgy" by S. Roberts.
What is important about these alloys is that they cannot be made by the more conventional ingot-casting processes in that the alloy ingredients tend to segregate into coarse constituents during solidification. The coarse intermetallic phases do not substantially contribute to strengthening of the alloy due to a large particle size and spacing. Generally, for dispersion strengthened alloys, particle spacings of one micrometer or less, are effective in increasing the strength of the matrix. In addition, retention of room temperature and elevated temperature strength upon elevated temperature exposure is desirable in aluminum alloys.
Therefore, it is a primary object of the subject invention to provide an aluminum alloy that has good mechanical properties up to 800.degree. F.
Another object of the subject invention is to provide an aluminum alloy that retains substantially all its room temperature mechanical properties after extended exposure to temperatures up to and including 800.degree. F.
It is further object of the subject invention to provide an aluminum alloy having superior compression strength in the 600.degree. F. temperature range, compared to existing dispersion strengthened aluminum alloys.